As shown in FIG. 6, in a conventional oven-controlled crystal oscillator (OCXO) 20, a circuit board 23 formed of glass epoxy resin is fitted to upper ends of, for example, four earth pins 22a and 22b arranged on a glass epoxy board 21 in a standing condition, a metal plate 24 is fitted to a lower face of the circuit board 23 via a radiation sheet 25, and further, a crystal resonator 26 is fitted to a lower face of the metal plate 24. Moreover, an electronic part 27 such as a circuit element is mounted on an upper face of the circuit board 23, and terminals 29 of the crystal resonator 26 are provided in a protruding condition. Furthermore, the glass epoxy board 21 is covered with a metal cover 28, and the metal cover 28 is soldered at a plurality of positions W (for example, two positions) on an outer peripheral edge of the glass epoxy board 21 and sealed.